As in Once, Carney tells a music-infused love story that isn't actually a romance, but rather a tale of two people who lift each other at a time of need. Fans of Once may find this somewhat derivative, although the cast and location give it a witty, emotional twist, and the songs are still gorgeous.

Songwriter Greta (Knightley) has just been dumped by her rising-rockstar boyfriend Dave (Levine) when her pal Steve (Corden) coaxes her into singing at an open-mic night in a New York bar. In the audience is has-been music producer Dan (Ruffalo), who in Greta sees an artist who deserves to be making records. Both have nothing to lose, so embark on a recording project without the help of Dan's record-label partner Saul (Bey, aka Mos Def). Meanwhile, Dan is trying to reconnect with his estranged wife and teen daughter (Keener and Steinfeld).

Despite the naggingly familiar story, there's a freshness to these characters and situations. Knightley and Ruffalo may be an odd couple, but they have easy chemistry that's even more disarming since it's Knightley who delivers the more effortless performance. Ruffalo plays up Dan's scruffy, rock-bottom persona, adding an intriguing edge of desperation to Dan's against-the-grain confidence. Knightley has rarely been this relaxed on-screen, letting her own sparky personality come through winningly, as well as considerable musical talent.

As with Once, this is a movie about the expressive power of music to boost a troubled soul. Carney inventively gets into Dan's reveal what he sees in raw, undeveloped talent, a slightly gimmicky trick that works beautifully. And the songs are performed with raw emotion by both Knightley and Levine, who bolsters the emotional stakes with a solid, albeit not-too-demanding, supporting turn. Corden and Keener are also good in roles they've played before, as are lively side performers Bey, Green and Morrow.

Carney shoots the film with loose honesty, keeping the tone witty and enjoyably messy, while adding a nice New York sensibility. The songs don't feel fully interwoven with the story, and the father-daughter subplot feels sometimes distracting, but the actors' engaging improv-style performances are easy to identify with. This is also a gently pointed look at a recording industry that's drifted from real music to pre-packaged video stars with social media cred. So the way Greta records and releases her music feels almost wistful.